Electrical gunsight superelevation and roll correcting device



P. R. WHEELR ELECTRICAL GUNSIGHT SUPERELEVATI ON AND Jan. 23, 1951 ROLL CORRECTING DEVICE Filed Dec. 19, 1945 5 Sheets-Sheet 1 his lb QS www# m h5 .SSQ

INVENTOR PHlLL/P R; WHEHLER ATTORNEY Jan. 23, 1951 P. R. WHEELER 2,538,821

' ELECTRICAL GUNSIGI-IT SUPERELEVATION AND ROLL CORRECTING DEVICE Filed Dec. 19, 1945 5 Sheets-Sheet 2 Y m O3( N l INVENTOR P19/LIP R WHEEL ER ATTORNEY Jan. 23, 1951 P. R. WHEELER 2,538,821

ELECTRICAL CUNsICHT suPERELEvATIoN AND ROLL CCRRECTINC DEVICE 5 Shets-Sheet 3 Filed Dec. 19, 1945 INVENTOR IP n; WHEELER Y M ATTORNEY Patented Jan. 23, 1951 UNITED STATES PATENT OFFICE ELECTRICAL GUNSIGHT SUPERELEVA'YIION AND ROLL -CORRECTING DEVICE amended April 30, 1928; 370 0. G. 757) The present invention relates to gun sights and particularly to an improved gun sight superelevation and roll control device to be employed in sights operating on the disturbed-line-of-sight principle. Sights of this general character are described in the following 'United States patents: 1,322,153, JQS. Wilson and W. E. Dalby, issued November 18, 1919; 2,183,530, Robert Alkan, issued December 19, 1939; 1,724,093, Robert Kauch and Charles L. Paulus, issued August 13, 1929.

The present application is a continuation-inpart of my abandoned patent application, Serial Number 510,403 entitled Cathode-ray Gun Sight and filed in the U. S. Patent Office on No vember 15, 1943.

When a gunner establishes a line of sight on a moving target, he must lead the target by a suitable angle. That is, the weapon must be so pointed that the line of fire leads the line of sight. This leading is accomplished by the target velocity corrections of the sight setting. In the absence of these corrections the projectile would pass behind the target. The lead angle depends on the target velocity and the time of ight of the projectile, the last-mentioned parameter varying almost linearly with range for short ranges. The gunner must allow also for the effect of gravity on the `projectile. In other words, he must elevate the gun above the direct line of sight to the target to allow for the drop of the projectile after it leaves the gun muzzle. This is accomplished by the superelevation corrections of the sight setting. Superelevation to correct for gravity is functionally related to range and varies as `the cosine of the angle of elevation. In gun sights which operate on the disturbedlineeof-sight principle the gunner maintains the line of sight on a target by tracking the target and as he does so he manually positions the gun and sight housing. The required target velocity and superelevation corrections furnish a basis for angularly so disturbing the line of sight with respect to the line of nre that when the line of sight is maintained on the target the line of nre is appropriate to score a hit. Y

It is an object of the present invention to provide an improved and simple electrical arrangement for automatically applying superelevation and target-elevational-velocity-component corrections to a gun sightrof the type having aV dis- 2 flcation, to the claims appended thereto, and to the accompanying drawings in which:

Fig. 1 comprises a geometrical presentation of the target velocity computation;

Fig. 2 comprises a'geometrical presentation of the superelevation computation;

Fig. 3 comprises a gun and sight including a superelevation and roll control device in accordance with my invention;

Figs. 4, 5 and 6 comprise, respectively, a detailed perspective view of the pendulous member of my correcting device, an elevational sectional view taken on line 5-5 of Fig. 6, and looking in the direction of the arrows, and an elevational sectional view taken on line 6-6 of Fig. 5.

Fig. 7 comprises a diagram of the electrical circuits of my device.

Fig. 1 shows the essential features of the short range re control problem. A gun Il is fired at an airplane I2. At the instant of fire the airplane is at a position called the present position. The gun should be pointed at some later position of the target called the future position, such that the projectile will reach the future position at the same time as the target. The angle between the line from the gun to the present target position (or line of sight) and the line from the gun to the future position (or line of fire) is the lead angle. This lead angle has components in elevation and azimuth. One of the parameters upon which the proper lead angle and sight setting are premised is the component of target velocity in the plane of elevation.

The angular velocity of the target as observed from a gun on a stationary platform is the an-V gular movement of the target about the gun per second of time. The time of flight is obviously the time taken by a projectile to reach the target. The total angular motion of the target during the time of flight is equal approximately to the angular velocity of the target at the present position multiplied by the time of flight in seconds. Other quantities involved in the lead-computing fire control problem, such as present and future slant range are appropriately labeled in Fig. 1. It will be seen that range or time of flight is a second parameter in part determinative of the appropriate elevational sight setting.

1f the gun bore is pointed at the future position of the target without further correction the projectile would then fall below the target because of the downward force of gravity. To compensate for this undesired effect of gravity the gun elevation is increased by an additional angle herein called the superelevation angle, as illus- Superelevation=constant time of iiightX cosine of gun elevation In my copending application entitled Gun Sight Superelevation Control Device, Ser. No. 636,045 filed in the U. S. Patent Oice on December 19, 1945, now Patent 2,504,168 granted April 18, 1950, there is shown a gun sight of the type in which a reference mark is electrically deflected, not only for the purpose of introducing the target velocity correction, but also forthe purpose of introducing the superelevation correction and thus overcoming the undesired effects of gravity. In my copending patent application, Serial No. 636,047, entitled Cathode Ray Tube Gun Sight, and filed in the U. S. Patent Oice on December 19, 1945, now Patent 2,459,206 granted January 18, 1949, there is shown a gun sight providing for both target velocity and superelevation corrections.

It will be noted that the discussionv of the fire .v

control problem has to this point been premised on the assumption that the gun is mounted on a stationary platform. If a gun is mounted aboard a ship, which is Subject to rolling, pitching', and yawing, the problem of introducing a correction for the rate of generation of the level angle is introduced. In my above-mentioned copending patent application entitled, Gun Sight Superelevation Control Device, the superelevation signal is referred to the true horizontal plane, but the target-elevational-velocity-component signal is obtained from a generator which produces a signal proportional to rate of motion of the gun about the supporting plane in tracking the target. This signal is a function of the rat-e of angular movement of the gun about trunnions which are fixed to this supporting plane. This angular movement is functionally related to target velocity when the supporting plane is stationary, but when the supporting plane rolls, thenA an arrangement for generating a signal proportional to rate of motion of the gun about the true horizontal is required.

In my copending patent` application entitled Gyroscopically Controlled Electrical Gun Sight, Ser. No. 636,048 filed in 'the U. S. Patent Oiiice on December 19, 1945, there is shown a system which provides for the introduction of corrections to compensate both for roll and pitch (i. e. for both level angle and cross-level angle generating rates). The instant application also represents a step forward in the art but along a different route and it is addressed to the correction of superelevation and roll.

The apparent elevational component of target velocity as it appears to a gunner is related .not only to target velocity but also to the time rate of change of the level angle or angle of roll. The level or roll angle is measured about an axis in the true horizontal plane. It is the angle between the true horizontal plane andthe supporting deck plane, measured in a vertical plane through the line of sight.

Let it be assumed that fireis being directed athwartships at a stationary target. Let it also be assumed that the ship is rolling upwardly so that the gunner moves the gun and sight relative to the deck in keeping the line of sight on the target. In such a case it is manifest that no correction for an elevational component of velocity of the target is required. However, in a sight such as that shown in my copending application entitled Gun Sight Superelevation Control Device, and operating under such an assumed set of facts the gun would be turning about the trunnions and the action of the elevation generator would be such as to introduce an undesired disturbance of the line of sight with respect to the line of fire. It will be seen that when the trunnions are supported on a stationary horizontal platform the elevational rate of tracking of the target is linearly functionally related to target velocity. However, when the gun is mounted on a platform which rolls and introduces the generation of a llevel angle into the fire-control problem, then the tracking of the target must be referred to the true horizontal, that is, it must be functionally related to the motion between the gun and the true horizontal.

plane, rather than the motion between the gun and the supporting plane. In the case of a gun mounted on a rolling ship, the generated signals for the elevational-component-of-target-velocity-correction should be obtained from a generator which produces a signal functionally related to the rate of generation of the angle between the gun and the true horizontal rather than a signal functionally related to the rate of generation of with reference to the line of fire by introducing an undesired elevational-component-of-targetprovides a reference mark on which a target is` viewed and means responsive to dynamic movement of the gun in azimuth for moving the refer-- ence mark in azimuth. The system also comprises my novel gun sight superelevation and rollcorrecting device and this device comprises means responsive to dynamic movement of the gun in elevation with reference to a fixed frame of coordinates for moving the reference mark in elevation by an amount functionally related to the rate of such movement and means for displacingthe reference mark in elevation by an additional.

amount functionally related to the elevational position of the gun with respect to a fixed frame of coordinates.

The system disclosed in Fig. 3 may be brieflyV improved electrical gun sight superelevation fire 29.

and roll correcting device for the elevation generator and the gun sight superelevation cont-rol device there illustrated. Specifically, however, a gun II is mounted for turning in elevation on trunnions (one of which has the reference numeral I3) journaled in bearings on suitable supports I4,'I5. The gun is suitably mounted for movement in train (azimuth) by reason of the fact that the supports UI, i5 are secured to a turnable platform I6. The Fig. 3 embodiment also includesautomatic compensating sighting apparatus for use in combination with the gun, this apparatus being generally designated by the numeral I1. The sighting apparatus comprises a telescope casing I8, a back sight member or reference mark I9 comprising movable crosshairs and 2l, a front sight 22, and other desired optical elements (not shown). The reference mark provided by the intersection of the crcsshairs 2D and 2| is centered in the peep or arcuate notch V23 on the front sight 22, as viewed by the eye 24 of the gunner and a line of sight 25 is in this manner defined from the operators eyefto the target. In placing the line of sight on a target the operator grasps the handles 26, 21 and swings the gun in elevation and train while keeping the line of sight defined 'by the reference mark and by peep Z3 on the target, the reference mark being superimposed on the target.

It will be noted that the gun defines a line o The target-velocity, ships roll, range, and superelevation correction are developed in the sighting apparatus in such a manner as to govern the position of the reference mark provided by the intersection of crosshairs 2i), 2i and thus to disturb the line of sight with reference to the line of nre. By keeping the disturbed line of sight on the target the operator then automatically manually maintains the line of re in a correct position. The gun II, trunnions I3, supports le, I5, turntable IS, telescope casing I8, crosshairs 20, 2! and front sight 22 are individually of the prior art and schematically shown. Any suitable arrangements for performing the same functions may be substituted for them.`

The Fig. 3 embodiment also includes prior-art means responsive to dynamic movement of the gun in azimuth for moving the reference mark in azimuth for the purpose of introducing that component of the lead angle which is functionally related to the train vcomponent of target velocity and range. This` means includes a ccnventional reversible generator 3| for generating a direct-current electrical signal-voltage representative of the rate of tracking of the target in train (i. e., the component of target velocity in the plane of train or slant plane), My improved electrical gun sight superelevation and roll correcting device indicated generally by the numeral 32 on Fig. 3 (and described in detail in connection with the explanation of Figs. 4, 5 and 6) generates an electrical signal voltage representative of the elevational component of the target velocity (i. e., the tracking range in eleva tion). The output circuits of these generators are individuallygcoupled to variable voltage die viders 33 and 34 (Fig. 7). The output of voltage divider 33 is coupled to a galvanorneter 35 and the output of voltage divider 34 is coupled to a galvano-meter 35.` The sliding contacts 37,33 of potentiometers 33 and 34 are ganged by any suitable expedient indicated by the dashed line 39 .f 6 and galvanometer 36 positions crosshair 2i. The operation of elements 3i, the generator part oi 32, 33, 34, 35, 35, 37, 38 and 39, is such as to cause the reference mark to be positioned in elevation and in azimuth in coordination with the movements of the gun in elevation and in azimuth and thus to introduce the proper lead angle by causing the reference mark to be so posi- Ftionecl that the line of fire leads the line of sight. With the lexception of unit 32, elements Ei-" are of the prior art and further description .thereof is deemed unnecessary. A suitable generator corresponding to generator 3i is shown in the above mentioned U. S. Patent No. 1,322,153. Suitable galvanometers and crcsshair arrangements corresponding to elements 23, 2l, 35 and '36 are shown in the above mentioned U. S. Pat- -ent No. 1,724,093.

'Ihe rotor of train generator 3i is ycoupled. to turntable I 6 by any suitable mechanical expedient indicated by the dashed line di in such manner as to cause the generator rotor to move in coordination with the movement of the gun in train. This generator may be secured adiacent `the turntable I6 by any suitable supports such as brackets (not shown). AThe elements of my sighting system so far described in detail and assigned numbers, taken in the aggregate, essentially constitute a sight as shown in the abovementioned U; S. Patent No. 1,724,093, gemodied by the substitution of the train genere-tor of the above mentioned U. S. Patent No. 1,322,153 for the hydraulic train lead computing arrangement shown in said U. S. Patent No. 1,724 G93, .and as further modified by the substitution my improved superelevation and roll correcting device 32 for the elevational lead computing arrangement shown in said U. S. Patent No. 1,724,093. This device performs not only the function of an elevation generator as that shown in U.' S. Patent No. 1,322,153 but also the additional functions of providing roll and superelevation correction.

Formed about the casing i8 is a suitable housing 44. The assembly of housing 4d and casing I8 is rigidly secured to the gun by suitable brackets 45, 45. Galvanoineter 35 comprises a circular magnet 48. This magnet influences lever 49 at the extremity of which is mounted crosshair 28. At least a part or" the current flowing in conductors and 5l passes through a coil 52 mounted near the fulcrum point of the lever 45. This arrangement causes the lever which controls crosshair 28 to move from the central position shown by an amount directly proportional to the amount of current flowing through the circuit and thus by an amount functionally related to the input signal applied thereto by train generator 3l. The movement 'is in a'direction dependent on the polarity of this' signal, Which polarity in turn depends upon the direction of train. Galvanometer 3e is similar fin construction and operation to galvanometer -line of re has a greater elevation than the line of sight; conversely, as a. descending target is tracked, crcsshair 2! is downwardly displaced and the leadansle correction tends to depress the line of nre with respect to the line of sight; similarly, as a target moving to the left is tracked, crosshair 20 is moved to the left and as a target moving to the right is tracked, crosshair 2i) is moved to the right. rIhus the problem posed by Fig. 1 is eifectively solved The range factor is introduced by positioning elements 31, 38 and 39 in a manner taught in the above mentioned U. S. Patent No. 1,322,153. For a given rate of target velocity, the deflection of the reference mark should be relatively small atshort ranges and relatively greater at longer ranges, as is well known to those skilled in the nre-control art.

The sighting arrangement also includes my improved superelevation and roll correcting device, shown in detail in Figs. 4, 5 and 6. For purposes of describing the construction and operation of the superelevation-correction portion of the device, it will be assumed that turntable i6 is at a stop and on the true horizontal and' that the trunnions I3, I3 are parallel to turntable I6. It will further be assumed that the line of fire provided by gun il is normal to the axis of the trunnions. The line of sight has already been disturbed in such a manner as to introduce corrections for target velocity. However, the solution of the problem posed in Fig. 2 requires a superelevation control for applying to the disturbing means (galvanometer 35) an electrical signal having a magnitude trigonometrically functionally related to the angle of the elevation of the gun, thereby to aotuate the galvanometer 35 to disturb the reference mark and the line of sight by an amount trigonometrically functionally related (as the cosine), to the angle of elevation. When such a superelevation control is provided the maintenance of the line of sight on a target causes the line of fire to be angularly elevated with respect to the line of sight by the amount of the desired superelevation correction. The means for supplying the superelevation-correction signals comprises a potentiometer 53, including a resistor 54 wound on an insulating and supporting form 55. The form is secured to segment 82 of a pendulous member indicated generally at 58 and comprising a weight-portion 59 integral with an arm 60. The pendulous member is pivotally secured to one of the trunnions i3 by a suitable bearing expedient indicated at El. rIihe pendulous member is angularly movable relative to gun El. Secured to the housing 62 is an insulating block on which is mounted a metallic contact element 63. Weight portion 59 maintains arm 5E] on the true vertical and the unit 32 is so arranged that contactor 63 is in the center of resistor 54 when the line of fire is parallel to the horizontal plane. Housing 62 is rigidly secured to gun Il.

A closed circuit (Fig. 7) is formed from contact 65, terminal B5, resistor 65, terminal 61, battery 5S, terminal 59 and that portion of resistor 54 between contact 63 and the terminal 69. Terminal 69 is connected to the midpoint of resistor 5G (as indicated by the letter Y).

and Contact 83 is at the midpoint on resistor 54, the full (positive, say) potentialof battery 88 is vimpressed across resistor 66. When the line of nre is elevated by 80, for example, resistors 56 and 54 are so proportioned that the potential appearing across resistor 65 is equal to the product or" 0.1736 and the full potential of battery 88. This potential is of the same polarity. lWhen the line of re is depressed from the horizontal by the potential of positive polarity then appearing When the i line of nre is parallel to the horizontal plane 8 across resistor 66 is equal to theproduct of 0.9848 and the full potential of battery 68. 'I'he two halves of resistor 54 are therefore not uniformly distributed and resistor 54 is so wound that the variation of resistance as contact .63 moves from terminal 69 to terminal 12 is not linear, but varies in accordance with a cosine function of the angle of elevation. VThe angle of elevation is the angle between the line of fire and the horizontal plane as measured in a plane perpendicular to trunnions i3 and the horizontal plane. Additionally, the resistor winding portion between terminals 69 and '13 is also so shaped that the potential impressed across resistor 68 varies in accordancewith a cosine function of the angle of depression of the line of fire 29. The output portion of voltage divider 34 and the output portion of resistor 68. are connected in series by conductor 15 and the terminals 38, 16 of this series combination are coupled to galvanorneter 35. The output potential of voltage divider 34 causes the behavior of crosshair 2i to be determined in part by the elevational component of the velocity of the target and range as explained hereinabove. The output potential appearing in resistor 156 causes the behavior of galvonometer S6' and the crosshair 2i also to be determined in part by the elevation of the target. Therefore, the position of crosshair 2i is a function of two arguments, the rst of these arguments being a rate or dynamic condition and the second' being a position or static condition. Additionally, Vthe rst of these arguments is in turn a function of two parameters: motion of own Ship and ymotion of the target.

As described above, the ganging of contacts '5i and 33 by expedient 39 provides a range adjustment. Since the superelevation correction is also functionally related to range there is provided a sliding contact i6 on the potentiometer whch includes resistor $6. lThis sliding contact is ganged with sliding contacts 3! and 8S by any suitable expedient indicated by the dashed line 53, to the end that the range adjustments for target velocity and for superelevation may be made by one operation.

In explaining the operation of the above described superelevation control portion or" my improved superelevation and the roll correcting device, it will be assumed that the interior and'exterior ballistics have been determined, that range tables are available, that the characteristics of the gun and the projectile are known, and that a selected stationary target is depressed from the horizontal plane and located on a linenormal to trunnion I3. For purposes of simpicity it will be assumed that the target position is such that a hit is mathematically' predictable if the line of re 29 is horizontal. Under that assumed condition, gravity is exercising its maximum effect on the projectile. The sight is therefore so adjusted that contact 53 is at terminal 59 and the f* potential of battery 5i. appears across the resistor 86. -Crosshair 2l) is then centered within tube *laand c rosshair 2l is vmoved from center by ad- Ijustn'ient of galvan'ometer 3 5 while thel gun is 'held stationary, inorder to align the eye or" the operator 24, the reference mark formed by the intersection of the crosshairs, the peep E3 and the target. The line of sight is then on the target and a hit should be scored when the gun is fired. The line of sight is disturbed to a maximum extent for any given range, under this condition. rNow let it be assumed that lire should be directed to .another target whicli'is stationary and located immediately above and at 90 of elevation to the gun. Under that condition the potential appearing across resistor-66 is 0, contact 63 is at terminal 1 2, and the reference mark provided by crosshairs 20 and 2| is centered in tube |8, so that the line of ire is not disturbed. The distance of the gun from target may be regarded as infinite with respect'tol the distance between casing I8 and the gun. Between these two terminal conditions (when ring on targets between and 90 of elevation) the voltage appearing across resistor 66 is trigonometrically functionally related to and varies asV the cosine of the angle of elevation. The range adjustment is provided by the gauging expedient 18 which adjusts the position of sliding contact 16.

In practice, the ballistics of the gun and the prodectile are obtained from range tables. The re control problem is capable of mathematical solution and the characteristics of the train and elevation units 3| and 32, resistor 66, resistor 54, and voltage dividers :i3-34,' and 66-16, as well as those of galvanometers 35 and 36 are mathematically determinable, so that speciiic circuits parameters are a matter of specic engineering design and depend upon the individual requirements for the system to be used, as will beclearly understood by those skilled in the art.

Figs. 4, 5 and 6 illustrate further details of my improved electrical gun sight superelevation and roll correcting device. A pendulum 58 is mounted on pivot 6| in housing 62. The housing is rigid.y secured to gun I| (Fig. 3). The pendulum .has a weight 59 located below the pivot and has an arcuate sheet of` copper, aluminum or other conductor 8| located at its lower end. The sheet 8| comprises an arc of a circle having the pivot 6| as its center. On the upper arm of the pendulum is an arcuate segment 82 which is formed as an arc of a circle having the pivot El at its center but having a smaller diameter than the arc of sheet 8|. Segment 82 is T-shaped at each end in order to support the forms on which coils of wire 54 and 83 are wound. As hereinabove described, winding 54 comprises the resistor portion of the superelevation control potentiometer. Winding 83 comprises the armature winding of the elevation generator. The armature winding 83 is positioned to move between the poles of a magnet 84, this magnet being rigidly secured to housing 62. The motion of the coil of wire 83 in moving between the poles of the magnet as gun l| is elevated or depressed causes a voltage to be generated in the coil 83 which is then conveyed by suitable wiring 85, 86 to potentiometer 34.

A resilient contact 63, rigidly secured to housing 62 and properly insulated bears against the coil 54 to form the superelevation control potentiometer, thev contact and the coil being connected to the galvanometer 36 by the wiring arrangement hereinabove described. The coil 83 is wound on and insulated from a metallic form 89. A magnet 88 is positioned in the lower part of the pendulum housing 62 so that the segment 8| moves between its poles. The purpose of magnet 88 and segment 8| is to provide desired damping of the oscillation of the pendulum.

The output voltage from the pendulum con-V trolled generator comprising elements 83 and 84 is combined with the output from the superelevation correction potentiometer and applied 10 tothe. elevation galvanometer 36. as. indicated above.

Returning now to the hypothetical situation posed hereinabove, let it. be .assumed that the 5 gunner does. not move the gun. li relative to the true horizontal in maintaining a line of sight on a stationary target. Under that assumed set of facts pendulum 58 does not move, coil 83 does not. move relative to magnet 8.4 and no 10 target elevational velocity component signal appears across conductors 85, 86. This is a desired condition. The output signal of the ele,- vation generatn1 is therefore referred to the true horizontal. That is, this generator generates a l5 Voltage which is proportiQllafl to the rate of the motion of gun in the elevational plane with respect to the true horizontal- While there has been shown and described what is at present considered te be a preferred embodiment of the invention, it will be obvious to those skilled in the art that various modifications and changes may be made therein without departing from the true scope of the invention. And it is, accordingly, intend-ed in the appended claims to cover all Such changes and modifications as fall within the true scope of the invention and without the proper scope of the prior art.

The invention herein described may be manufactured and used by orfor the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. in combination with a gun movable in planes of elevation and train, a gunsight adapted to move in unison with said gun comprising electrical means for providing a reference mark in the line of sight of a gunner movable in two mutually perpendicular directions each substantially normal to said line of sight in response to a first and second electrical quantity, means responsive to the dynamic movement of the gun in train for developing said first electrical quantity v 4:5 of magnitude proportional` to the rate of said movement, circuit connections for applying said value to said electrical means to cause movement of said reference mark in a direction substantially normal to the plane of elevation and opposite the direction of train, stabilizing means mounted on said gun for establishing a plane of reference, means moveable about said stabilizing means for developing said second electrical quantity comprised of the algebraic sum of a first component and a second component, said rst component being produced by the dynamic movement of said gun in the plane of elevation relative to said reference plane and of a magnitude proportional to the rate of said movement, said sec; ond component being produced by the angular position of said gun in the plane of elevation relative to said reference plane and of a magnitude proportional to the cosine thereof, and circuit connections for applying said second electrical quantity to said electrical means to cause movement of said reference mark in a direction parallel to the plane of elevation of said gun.

2. The combination defined in claim 1 above wherein said circuit connections contain adjustf able impedance means whereby the magnitude of said first and second quantities may be altered in accordance with changes in the range to said target.

3. The combination dened in claim 1 wherein said stabilizing means comprises a damped pen- Y 1l dulous means, said rst component producing means comprises respectively a generator having an armature winding and a eld producing magnet, and said second component producing means comprises a potentiometer coupled to a voltage source having a moving contact and resistor portion, said Winding and resistor portion being supported by said. damped pendulous means, said stabilizing means being further characterized by the addition of a housing for said pendulous means secured to said gun for movement about said pendulous means on movement of said gun in the plane of elevation, Said housing supporting said contact and said magnet.

PHILLIP ROOD WHEELER.

REFERENCES CITED Number Number 12, UNITED STATES PATENTS' Name Date n h Long Dec. 2, 1862 Brackett Nov. 6, 1883 Zeitlin June 22, 1943 Doyle et a1 May '7, 1946 Pontius et al Oct. 1, 1946 Pontiusvet a1 Sept.,2, 1947 Ketay Oct. 21, 1947 Wheeler Dec. 14, 1948 Wheeler Jan. 18, 1949 Gittens Mar. 8, 1949 Johnson Apr. 19, 1949 FOREIGN PATENTS Country Date Great Britain May 30, 1923 

